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Proceedings Paper

Development of large-aperture monolithic sapphire optical windows
Author(s): Joel Askinazi; Richard V. Wientzen; Chandra P. Khattak
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Paper Abstract

Large aperture (20-inch diameter) sapphire optical windows have been identified as a key element of new and/or upgraded airborne electro-optical systems. As has been recently reported, Crystal Systems continues in the development of the technology to grow 20-inch diameter, single crystal sapphire boules to meet this need. Owing to the spatial variations in the optical index of refraction potentially anticipated within 20-inch diameter sapphire crystals, computer controlled optical finishing has been identified as a key technology that may be required to enable achievement of transmitted wavefront errors of much less than 0.1 wave rms. BFGoodrich has developed this technology and has previously applied it to finish 8-inch- diameter sapphire optical windows to a transmitted wavefront error of at least four times better than the above requirement. As a key step in the scaling of these critical window technologies to produce 20-inch-diameter sapphire windows, BFGoodrich and Crystal Systems collaborated to apply these technologies to produce a 13-inch-diameter sapphire window having a transmitted wavefront error of 0.059 wave rms. Optical testing of this 13-inch sapphire crystal revealed that it possessed excellent refractive index homogeneity; far better than had previously been encountered in finishing 8-inch sapphire windows. This improvement in material quality implied that conventional optical finishing could potentially have been employed to finish this window to the 0.059 wave rms error. However, due to our desire to demonstrate the process technology for potential future application to 20-inch diameter sapphire windows, it was fabricated using computer controlled optical finishing. This paper addresses the results of this effort, the lessons learned, and the implications associated with the scaling of these technologies to 20-inch-diameter sapphire optical windows.

Paper Details

Date Published: 7 September 2001
PDF: 11 pages
Proc. SPIE 4375, Window and Dome Technologies and Materials VII, (7 September 2001); doi: 10.1117/12.439163
Show Author Affiliations
Joel Askinazi, BFGoodrich Co. (United States)
Richard V. Wientzen, BFGoodrich Co. (United States)
Chandra P. Khattak, Crystal Systems, Inc. (United States)

Published in SPIE Proceedings Vol. 4375:
Window and Dome Technologies and Materials VII
Randal W. Tustison, Editor(s)

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